1// Copyright 2016 PDFium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef CORE_FXCRT_MAYBE_OWNED_H_
6#define CORE_FXCRT_MAYBE_OWNED_H_
7
8#include <algorithm>
9#include <memory>
10#include <utility>
11
12#include "core/fxcrt/fx_memory.h"
13#include "core/fxcrt/fx_system.h"
14
15namespace fxcrt {
16
17// A template that can hold either owned or unowned references, and cleans up
18// appropriately.  Possibly the most pernicious anti-pattern imaginable, but
19// it crops up throughout the codebase due to a desire to avoid copying-in
20// objects or data.
21template <typename T, typename D = std::default_delete<T>>
22class MaybeOwned {
23 public:
24  MaybeOwned() : m_pObj(nullptr) {}
25  explicit MaybeOwned(T* ptr) : m_pObj(ptr) {}
26  explicit MaybeOwned(std::unique_ptr<T, D> ptr)
27      : m_pOwnedObj(std::move(ptr)), m_pObj(m_pOwnedObj.get()) {}
28
29  MaybeOwned(const MaybeOwned& that) = delete;
30  MaybeOwned(MaybeOwned&& that) noexcept
31      : m_pOwnedObj(that.m_pOwnedObj.release()), m_pObj(that.m_pObj) {
32    that.m_pObj = nullptr;
33  }
34
35  void Reset(std::unique_ptr<T, D> ptr) {
36    m_pOwnedObj = std::move(ptr);
37    m_pObj = m_pOwnedObj.get();
38  }
39  void Reset(T* ptr = nullptr) {
40    m_pOwnedObj.reset();
41    m_pObj = ptr;
42  }
43
44  bool IsOwned() const { return !!m_pOwnedObj; }
45  T* Get() const { return m_pObj; }
46  std::unique_ptr<T, D> Release() {
47    ASSERT(IsOwned());
48    return std::move(m_pOwnedObj);
49  }
50
51  MaybeOwned& operator=(const MaybeOwned& that) = delete;
52  MaybeOwned& operator=(MaybeOwned&& that) {
53    m_pOwnedObj = std::move(that.m_pOwnedObj);
54    m_pObj = that.m_pObj;
55    that.m_pObj = nullptr;
56    return *this;
57  }
58  MaybeOwned& operator=(T* ptr) {
59    Reset(ptr);
60    return *this;
61  }
62  MaybeOwned& operator=(std::unique_ptr<T, D> ptr) {
63    Reset(std::move(ptr));
64    return *this;
65  }
66
67  bool operator==(const MaybeOwned& that) const { return Get() == that.Get(); }
68  bool operator==(const std::unique_ptr<T, D>& ptr) const {
69    return Get() == ptr.get();
70  }
71  bool operator==(T* ptr) const { return Get() == ptr; }
72
73  bool operator!=(const MaybeOwned& that) const { return !(*this == that); }
74  bool operator!=(const std::unique_ptr<T, D> ptr) const {
75    return !(*this == ptr);
76  }
77  bool operator!=(T* ptr) const { return !(*this == ptr); }
78
79  explicit operator bool() const { return !!m_pObj; }
80  T& operator*() const { return *m_pObj; }
81  T* operator->() const { return m_pObj; }
82
83 private:
84  std::unique_ptr<T, D> m_pOwnedObj;
85  T* m_pObj;
86};
87
88}  // namespace fxcrt
89
90using fxcrt::MaybeOwned;
91
92#endif  // CORE_FXCRT_MAYBE_OWNED_H_
93